Rodents (rats and mice) annually consume and contaminate about 20 percent of the world's food supply. Without pest control, half of our food might be destroyed by crop and stored product pests. Rodents also do untold damage to property -- their gnawing is a suspected cause of fires attributed to unknown causes. As for insects, termites alone cost Americans about .5 billion each year in damage repair and control -- more than the combined cost of all natural disasters.
Pest tolerance in crop land is usually based on the cost of control. Sometimes pests can be numerous and do considerable damage to a crop before the cost of that damage outweighs the cost of control. However, we are less tolerant of pests in the urban environment. Most of us are very concerned upon finding insects living with us, so much that the presence of a single cockroach or flea will prompt pest control in the home